When a liquid sample is analyzed to measure the transmission characteristics such as transmittance and absorbency, by a spectrophotometer such as an ultraviolet-visible spectrophotometer, a prism or cylindrical-shaped cuvette for holding the liquid sample is normally used. An inner volume of a cuvette is normally several milliliters or more, and thus it is necessary to prepare a liquid sample in a sufficient amount to fill the cuvette.
Recently, an ultraviolet-visible spectrophotometer has been often used for determining protein or DNA quantity in the field of biochemistry. However, in many cases, the amount of a liquid sample to be analyzed is extremely small. Especially, since samples are precious and expensive in a DNA-related analysis, it is sometimes necessary to analyze a liquid sample in an amount of less than several microliters. Therefore, the aforementioned cuvette cell cannot be used for the analysis of a trace liquid sample.
As a device for spectrophotometric analysis of a trace liquid sample, Spectrophotometer ND-1000 distributed by NanoDrop Technologies LLC is conventionally known (see Non-Patent Document 1). As shown in FIG. 8, the spectrophotometer is configured such that a liquid sample 54 bridges, owing to the surface tension, the space between an upper base portion 50 and a lower base portion 52, which are vertically provided face to face with a predetermined distance in between. A measuring light irradiated from a light emitting-side optical fiber 51 installed in the upper base portion 50 is allowed to pass through the liquid sample 54 and the transmitted light is received by a light receiving-side optical fiber 53 installed in the lower base portion 52. The optical path length in the liquid sample 54 is set to approximately 1 mm, and hence analysis of a liquid sample in a trace amount of approximately 1 to 2 μL is said to be possible.
However, according to the aforementioned conventional spectrophotometer, after the analysis of one sample, it is necessary for cleaning purposes to wipe the end faces of both the light emitting-side optical fiber and the light receiving-side optical fiber by using, for example, a laboratory paper, before analysis of a next sample. This operation is a troublesome task, because it needs to be performed manually every time analysis of one sample is finished. Moreover, there is a problem of low throughput, since it is not possible to measure a plurality of samples while automatically changing the samples.
Non-Patent Document 1: NanoDrop ND-1000 Overview (online), NanoDrop Technologies LLC, U.S., searched on Mar. 15, 2006 on the Internet <URL: http://www.nanodrop.com/nd-1000-overview.html>